Switched reluctance machines have become increasingly popular in recent years. In a switched reluctance motor, a stator has sets of poles that are sequentially energised to rotate a rotor into line with the energised pair of poles, under the influence of the magnetic fields associated with each set of poles. By rapidly switching between different pairs of poles, it is possible to cause the rotor to rotate at a very high speed.
Recent developments in switched reluctance motors have resulted in higher speeds of rotation of the rotor than was achievable hitherto. However, control of the rotor at such high speeds can be problematic. In particular, the angular position of the rotor at which the poles are energised and de-energised needs to be controlled carefully.
It has been proposed to employ control law tables, held in a memory associated with the control circuits of the machine. The control law tables typically comprise look-up tables relating the turn-on and turn-off angles to the speed and torque of the machine over a wide range of operating conditions. However, such control law tables comprise a large amount of data, which thus require a large memory.